Display devices such as, for example, flat panel display devices typically utilize a cathode structure that is formed over a backplate. The cathode structure includes row electrodes and column electrodes that are used to activate regions of field emitters. The field emitters emit electrons that are directed towards respective pixel or sub-pixel regions on a faceplate. By selectively activating row electrodes and column electrodes, electrons are emitted that strike the respective pixel or sub-pixel regions on the faceplate. Typically, phosphors are coated on the inside of the faceplate. The electrons strike the phosphors, producing red, green or blue visible light that forms a visible display.
In prior art processing techniques, aluminum is commonly used for forming row electrodes and column electrodes. However, aluminum is subject to hillock formation. Hillock formation results in nonuniform planarization and can cause both row and column shorts to occur.
In one recent prior art process a layer of tantalum is deposited over the aluminum layer for reducing hillock formation. However, the resulting structure has a conductivity that is too low for use in large flat panel display devices. That is, though this process is sufficient for making small flat panel displays, the resulting row or column has too high a resistivity to be used in making large flat panel displays.
In prior art processes that use a layer of aluminum that is overlain by a layer of tantalum, the layer of aluminum is first deposited by placing the backplate into a sputtering chamber. Once the aluminum layer deposition is complete, the backplate is removed from the sputtering chamber. The layer of aluminum is then masked. More particularly, photoresist is deposited over the backplate, and the photoresist is exposed. The layer of aluminum is then etched using a wet etch process to form the desired aluminum structure.
The backplate is then placed into a second sputtering chamber that deposits the tantalum layer. Once the deposition of the tantalum layer is complete, the backplate is removed from the second sputtering chamber. The layer of tantalum is then masked. More particularly, photoresist is deposited over the backplate, and the photoresist is exposed. The tantalum layer is then etched. Because wet etch processes are not effective for etching tantalum, prior art processes must use a dry etch process. In one recent prior art process a reactive ion etch is used for etching the tantalum layer.
The use of two separate sputtering deposition steps is expensive and time consuming. Also, the use of two separate masking process steps is expensive and time consuming. These factors result in a low manufacturing yield and throughput. In addition, the steepness of the row USA electrodes and column electrodes of prior art processes results in manufacturing defects related to cracking of the overlying tantalum layer.
The dry etch process is complex. Also, the use of a dry etch process is expensive as it requires the use of expensive capital equipment (e.g. reactive ion etcher). Moreover, the dry etch process is corrosive to aluminum and can result in corrosion of the aluminum layer when pinholes are present in the tantalum layer. In addition, the dry etch process forms polymers within the tantalum layer. Thus, following the dry etch, a polymer strip process is required for removing the polymers. The polymer strip process is expensive. In addition, the corrosive dry etch process can result in pinholes in the glass backplate.
During subsequent conventional process steps, the column electrode is subjected to potential damage. More particularly damage often results from, ion bombardment, cavity etch, cone deposition, dielectric deposition, masking and etching of the dielectric layer, deposition and etch of a molybdenum layer, deposition and etch of a chromium layer, polyimide deposition, etc. These process steps lead to shorts and opens that result in reduced yield and device failure.
Another problem that occurs in prior art devices is column to focus waffle shorts. These column to focus waffle shorts lead to reduced yield and device failure. In addition, the electrodes used in prior art column electrodes can react with the frit seal in the frit seal region, leading to shorts between column electrodes.
Thus, a need exists for an electrode structure and a method for forming an electrode structure that does not result in hillock formation. Still another need exists for an electrode structure and a method for forming an electrode structure that meets the above-listed needs but which does not produce undesired electrical shorts or opens in the cathode structure. Still another need exists for an electrode structure and a method for forming an electrode structure that meets the above-listed needs and that is inexpensive to manufacture and that does not result in reduced yield.
As yet another drawback, during fabrication of one embodiment of a multilayer electrode, a two step etch process is employed. In the first step, an oxidizing agent is used to oxidize the multilayer stack from which the multilayer electrode is to be formed. Next, an etchant is used which readily removes the oxidized material. The etchant is used to form the multilayer electrode from the multilayer stack of material. Unfortunately, when using certain materials and under various circumstances, unwanted excess oxidation of the material comprising the multilayer stack can occur. This unwanted excess oxidation results in deleterious superfluous etching of the material in the multilayer stack. Hence, precise and controlled etching of the multilayer stack is compromised. Such compromising of the etching process can severely affect the formation of the electrode. In fact, “opens” or breaks in the multilayer electrode may result from unwanted excess oxidation and etching.
Thus, a need exists for a multilayer electrode and a method of forming such a multilayer electrode wherein the multilayer stack, from which the multilayer electrode is formed, is not subjected to unwanted excess oxidation during the electrode formation process. Still another need exists for a multilayer electrode and a method of forming such a multilayer electrode wherein the multilayer electrode does not suffer from excessive “opens” or breaks.
As still another drawback, during the formation of a multilayer electrode in a standard evacuated environment, it is possible to form intermetallic compounds. That is, the evacuated environment in which both layers of the multilayer stack is formed is conducive to the formation of intermetallic compounds. These intermetallic compounds are typically, formed when atoms and molecules of the two separate metal layers diffuse together to form a new compound. Unfortunately, these intermetallic compounds have oxidation and etch rates which can vary greatly from that of the constituents which comprise the intermetallic compounds. As a result, the formation of these intermetallic compounds can lead to variation and unpredictability in the subsequent oxidation and etching processes.
Thus, a need exists for a multilayer electrode and a method of forming such a multilayer electrode wherein the multilayer stack, from which the multilayer electrode is formed, does not suffer from significant formation of intermetallic compounds during the electrode formation process.